eternalimage,
i've started getting the same error as you with windows media player. everything was working fine for months, then something happened, havent been able to play any music or video files since. itunes shows no error, just wont play. other media players come up with different errors.

i tried system restore, which fixed the problem for a while. but it happened again and now i'm stuck. considering wiping everything and reinstalling vista.

have you had any luck? i'll post anything i find out.